1. Field of the Invention
This invention relates to a filament lamp and light-irradiation-type heat treatment device, and particularly, to a filament lamp used for heat treatment of an article and a light-irradiation-type heat treatment device equipped with such a filament lamp.
2. Description of Related Art
Heat treatment is used in a variety of processes in the manufacture of semiconductors, including film growth, oxidation, implantation of impurities, nitriding, film stabilization, silicidation, crystallization, and ion injection activation. In particular, rapid thermal processing (hereafter RTP) of a semiconductor wafer or other article to be treated by quickly raising and lowering its temperature enables improved throughput and quality, and so its use is desirable.
Light-irradiation-type heat treatment devices that can heat the article to be treated without contacting it, by means of light irradiation from a light source, such as an incandescent lamp with filaments arranged inside a light emitting bulb made of a material that is transparent to light, is widely used as heat treatment device used for RTP (see, JP-A-H7-37833 and JP-A-2002-203804 corresponding to U.S. Pat. No. 6,876,816).
By means of a light-irradiation-type heat treatment device of this type, it is possible to heat the article to be treated to a temperature of 1000° C. or higher in a period of from several seconds to several tens of seconds, and to cool the article quickly by stopping the light irradiation.
When using a light-irradiation-type heat treatment device of this type to perform RTP of semiconductor wafers, for example, unevenness of the temperature distribution of a semiconductor wafer when it is heated to a temperature of 1050° C. or higher is liable to cause a phenomenon called “slip” in the semiconductor wafer, in which crystal transition defects arise and quality declines, and so it becomes necessary to heat the semiconductor wafer, hold it at a high temperature, and then cool it so that the temperature distribution will be even across the entire surface.
Even in the event that the light irradiation is performed so that the degree of irradiation is even for semiconductor wafers that have the same treatment characteristics across the entire irradiated surface, at the edges of the semiconductor wafer, heat will be radiated by the side surfaces of the semiconductor wafer, and so the temperature at the edges of the semiconductor wafer will be reduced and there will be unevenness in the temperature distribution of the semiconductor wafer.
To resolve problems of this sort, there have been attempts to make up for the temperature drop due to heat radiation from the sides of the semiconductor wafer, and thus, even out the temperature distribution in the semiconductor wafer by means of light irradiation of the surface at the edges of the semiconductor wafer to a greater degree than the surface at the center of the semiconductor wafer.
However, there may be small, special regions in the article to be treated that are very small relative to the length of the emitted light of the incandescent lamp, and when light irradiation is performed at a light intensity appropriate to the characteristics of these special regions, the regions other than the special regions are irradiated under the same conditions, and so it has not been possible with earlier heat treatment device to adjust temperatures to provide suitable temperature conditions for both the special regions and the other regions, or in other words, to control only the degree of irradiation of the small, special regions so that the temperature status of the article to be treated will be even.
For example, it is common to form a film of metallic oxide or other material on the surface of a semiconductor wafer by the sputtering method and then dope it with impurities by means of ion implantation; the film thickness of such a metallic oxide and the density of the impurity ions will have a localized distribution on the surface of the semiconductor wafer. This localized distribution will not necessarily have central symmetry with respect to the center of the semiconductor wafer; sometimes, with regard to the density of the impurity ions, for example, the density of the impurity ions varies in small, special regions that do not have central symmetry with respect to the center of the semiconductor wafer.
Even in the event that light irradiation is performed so that there is the same degree of irradiation of such special regions and the other regions, there will be differences between them in the speed of temperature rise and the temperature in the special regions will not necessarily be the same as the temperature in other regions, and there may be the problem that the unwanted temperature distribution in the treatment temperature of the article being treated results in difficulty in giving the desired physical properties to the article being treated.
In view of that situation, the present inventors proposed a filament lamp with the following constitution, to be used as the light source of a light-irradiation-type heat treatment device (see the specification of Japanese patent application 2005-191222 and corresponding U.S. Patent Application Publication 2006-197454).
A filament lamp with this constitution has multiple filaments in a light emitting bulb and is constituted to enable individual control of the light emitted by each filament, so that, if it is used as a light source for heating in a light-irradiation-type heat treatment device, it is possible to arrange filaments with high precision with respect to the regions to be irradiated on the article to be treated, by aligning the filaments in parallel rows. Accordingly, by means of such light-irradiation-type heat treatment device, it is possible to supply power individually to the multiple filaments and to individually control the light emitted by each filament, and so it is possible to irradiate with the desired irradiation distribution according to the characteristics of the article to be treated even when the distribution of localized temperature variations on the article to receive heat treatment is non-symmetrical with respect to the article to be treated, with the result that the article to be treated can be heated evenly and an even temperature distribution can be achieved across the entire irradiated surface of the article to be treated.
In recent years, there have been demands for further improvement of throughput (improved processing efficiency) and quality in light-irradiation-type heat treatment devices. To meet these demands, it is considered necessary to further speed up the temperature rise characteristics of semiconductor wafers when filament lamps with the constitution described above are used as light sources; for example, it is considered possible to respond by supplying more power per unit length to the filament than in the past.
However, it was judged that, if the power supplied to the filament is simply increased, there is liable to be unwanted discharge between the leads of neighboring filament assemblies. If such unwanted discharge continues over a long period, there will be the defect of the filament or the lead melting through.
Further, as stated above, to make the temperature distribution even on the irradiated surface of the article to be treated, it is desirable that the filament assemblies be arranged so that the filaments are close to each other (with a small space between filaments), but the problem described above becomes marked with such a constitution.